Question

Direct mail advertisers send solicitations​ ("junk mail") to thousands of potential customers in the hope that some will buy the​ company's product. The response rate is usually quite low. Suppose a company wants to test the response to a new flyer and sends it to 1150 people randomly selected from their mailing list of over​ 200,000 people. They get orders from 114 of the recipients.

Create a 90​% confidence interval for the percentage of people the company contacts who may buy something.

Answer 1

n = 1150
x = 114
p = x/n
p = 114/1150 = 0.099
z critical value = ____

(Then, I got this formula from the question in the 'Related Questions' below. I hope this helps.)
E = za/2 *sqrt((p (1-p)/)/n))